The present invention relates to a video compression method which is employed in connection with the conditional replenishment transmission and receiving method. In the transmitter used in the method, those areas which are changed with respect to the previous image are detected and the respective picture information, together with the addresses of the respective areas, is transmitted into the transmission channel. In the receiver a new image is reconstructed on the basis of the previous image and the addresses of the changed picture areas as well as on the basis of the picture information representing the occurred changes.
A digitized video signal which contains the picture information and is transmitted by means of the pulse code modulation method, requires a transmission channel capacity, the magnitude whereof is defined on the basis of the amount of picture elements and grey scale levels as well as the number of images to be transmitted per second. The information to be transmitted can be decreased without deteriorating the quality of the image by transmitting only the video signal representing the change occurred in between successive images. Therefore it is necessary, in one way or another, to detect the areas in the image which are changed with respect to the previous image, and only these changed areas are then transmitted. The information concerning these transmitted changed picture areas must also be provided with addresses which denote the picture area in question. Thus it is possible to reconstruct every image in a true and accurate fashion.
In the transmitter applying the above explained method, two separate picture memories are needed, the first containing the new image and the second containing an image corresponding to that which was last reconstructed by the receiver. In the receiver, only one picture memory is needed, which is the display memory.